Organic EL elements have various advantages that they can be driven at low voltage, have high luminance and easily emit lights having various colors compared with inorganic EL elements. Thus, various studies have been performed to obtain the elements having superior properties. In particular, many attempts to obtain materials for each layer which constitutes the element have been reported.
In particular, it has been studied to use metal oxide as the layer such as an electron injection layer or a hole injection layer. For example, it has been described in Patent Document 1 that an inorganic oxide layer such as a molybdenum oxide layer is provided as a highly efficient electron injection layer between a light-emitting layer and an electron injection electrode.
In order to enhance a property of the organic EL element, it is necessary to laminate multiple layers having various functions. Here, when the layer containing a polymer compound is laminated, a so-called wet process is typically used in terms of production cost. That is, a step of applying a solution obtained by dissolving the polymer compound in a solvent is performed. However, there is a problem that the molybdenum oxide layer has a low durability to the wet process, as a result, it is difficult to form the layer containing the polymer compound on the molybdenum oxide layer by the wet process and it is hard to enhance a light-emitting property and a lifetime property of the resulting organic EL element.
Patent Document 1: JP 2002-367784-A